In general, the production of carbon black entails the cracking or thermal decomposition of a hydrocarbon feedstock in a reaction chamber at temperatures well above 2000.degree. F. (e.g., 3000.degree. F.). The carbon black entrained in the gases exiting the reaction chamber are then cooled in a quenching operation and then collected by any suitable means conventionally used in the art.
In the initial stages of reaction in the furnace, particles of carbon black are formed. These particles coalesce as the reaction continues and form much larger aggregates. During subsequent collection and densification stages in the carbon black manufacturing process, the aggregates pack together to form agglomerates. These agglomerates are often then further processed into pellets or beads in a separate pelletizing operation for ease in shipping of handling.
Carbon blacks have numerous uses with the major use being as a reinforcing agent or filler for the rubber and tire industries. Moreover, carbon black has seen increased use in other areas such as coloring agents and reprographic toners for copying machines. The various applications of carbon black necessitate a diverse range of carbon black characteristics such as particle size, structure, yield, surface area, and stain.
It is thus desirable to have a reactor which is adaptable for producing a wide assortment of different types of particle sizes and structure so as to handle various purchasing orders. That is, a reactor which is highly versatile avoids the disadvantage of having to rely upon a variety of different types of reactors to handle different orders. From a manufacturing standpoint, it is also desirable to have a reactor which is efficient in production (i.e., high yield) and capable of producing a high quality carbon black product while avoiding grit formation during the process.
Another consideration which is of importance in the production of carbon black is the avoidance of coke formation on the interior surface of the reactor as such coke formation tends to cause spalling of the inner refractory lining of the reactor. The coke and spalled refractory are contaminants and are highly undesirable in the product. In addition, the reactor should be user-likeable; in other words, easy to operate, easy to adjust for different uses and safe to operate. A carbon black reactor normally consists of different sections with special functions. These sections correspond with the different stages of the carbon black formation. The first section is the combustion section. It provides the energy necessary to crack the carbon black feedstock. A fuel, i.e. natural gas, is mixed with hot air for combustion and carbon black feedstock is then mixed with the hot combustion gases and carbon black is formed thereafter. The corresponding section is called the carbon black formation section, which is followed by the quench section. Depending on the desired carbon black grade a distinct residence time is necessary. The reaction is cut off by injecting water at different positions within the quench section.
A key feature to good reactor operation is a rapid and complete mixing of a high temperature combustion gas stream in with the carbon black feedstock. The temperature of the combustion gases being mixed with the feedstock should be maintained as uniform as possible such that the desired carbon black characteristics also remain highly uniform. The creation of a turbulent combustion gas flow in the area where the combustion gases intermix with the injected carbon black feedstock is one way to ensure a rapid and complete intermixing of the carbon black feedstock. However, in creating such turbulence care must be taken to ensure the combustion gases do not force the carbon black feedstock into contact with the interior walls of the reactor as such contact leads to coke formation. This coke formation problem was one of the disadvantages of the prior art reactors which utilized a vortex or tangential flow of the combustion gases as the swirling gases tended to impinge the newly introduced carbon black feedstock against the interior walls of the reactor.
Prior art reactors, such as that illustrated in U.S. Pat. No. 4,213,939, include axial flow reactors having the possibility of radial and axial introduction of carbon black feedstock. These reactors provide a certain degree of versatility in the types of carbon black capable of being produced, but suffer from the drawback of inadequate intermixing of the carbon black feedstock and axial flowing combustion gases due to a lack of turbulence in the flowing combustion gases.
Heller U.S. Pat. No. 2,851,337 discloses a process comprising the steps of generating hot combustion gases in a combustion chamber and passing the resultant gases through an elongated, unobstructed heat insulated chamber, gradually reducing the transverse area of the stream, injecting the hydrocarbon to be decomposed into the stream of hot gases passing through the constricted zone of the chamber and then gradually increasing the transverse area of the resultant stream as it continues through the chamber. The Heller patent, while perhaps providing a high velocity flow rate, fails to adequately create turbulence in the flow of combustion gas as the gas travels through the smooth, gradually curving design of the Heller reactor chamber.